Bi-directional parallel optical link

ABSTRACT

A system is disclosed. The system includes a first optical transceiver having a first set of transmitters and a first set of receivers and a second optical transceiver having a second set of transmitters coupled anti-symmetrically to the first set of receivers of the first optical transceiver and a second set of receivers coupled anti-symmetrically to the first set of transmitters of the first optical transceiver.

FIELD OF THE INVENTION

The present invention relates to fiber optic communications; moreparticularly, the present invention relates to spectrally combining anddividing fiber optic signals and arranging optical transmitters andreceivers for bi-directional communication.

BACKGROUND

In the future, optical input/output (I/O) will be used in computersystems to transmit data between system components. Optical I/O is ableto attain higher system bandwidth with lower electromagneticinterference than conventional I/O methods. In order to implementoptical I/O, radiant energy is coupled to a fiber optic waveguide froman optoelectronic integrated circuit (IC).

Typically, a fiber optic communication link includes a fiber optictransmitting device such as a laser, an optical interconnect link, and alight receiving element such as a photo detector. Currently, there is anincreasing objective to increase the bandwidth of optical interconnectlinks.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention. The drawings, however, should not be takento limit the invention to the specific embodiments, but are forexplanation and understanding only.

FIG. 1 illustrates one embodiment of a computer system; and

FIG. 2 illustrates one embodiment of an optical assembly;

FIG. 3 illustrates one embodiment of a bidirectional parallel opticallink; and

FIG. 4 illustrates another embodiment of a bidirectional paralleloptical link.

DETAILED DESCRIPTION

According to one embodiment, a mechanism to spectrally combine anddivide optical I/O is disclosed. Reference in the specification to “oneembodiment” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the invention. The appearancesof the phrase “in one embodiment” in various places in the specificationare not necessarily all referring to the same embodiment.

In the following description, numerous details are set forth. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

FIG. 1 is a block diagram of one embodiment of a computer system 100.Computer system 100 includes a central processing unit (CPU) 102 coupledto an interface 105. In one embodiment, CPU 102 is a processor in thePentium® family of processors including the Pentium® IV processorsavailable from Intel Corporation of Santa Clara, Calif. Alternatively,other CPUs may be used. In a further embodiment, CPU 102 may includemultiple processor cores.

According to one embodiment, interface 105 is a front side bus (FSB)that communicates with a control hub 110 component of a chipset 107.Control hub 110 includes a memory controller 112 that is coupled to amain system memory 115. Main system memory 115 stores data and sequencesof instructions and code represented by data signals that may beexecuted by CPU 102 or any other device included in system 100.

In one embodiment, main system memory 115 includes dynamic random accessmemory (DRAM); however, main system memory 115 may be implemented usingother memory types. According to one embodiment, control hub 110 alsoprovides an interface to input/output (I/O) devices within computersystem 100.

FIG. 2 illustrates one embodiment of an optical assembly 200. In such anembodiment, optical assembly 200 is implemented to couple optical I/Obetween components within computer system 100. For instance, opticalassembly 200 may couple optical I/O between CPU 102 and control hub 110,and/or control hub 110 and main memory 115. In other embodiments,optical assembly 200 may couple a component within computer system 100to another computer system.

Referring to FIG. 2, optical assembly 200 includes optical fibers 210,an array of lasers 220, an array of photo detectors 230 and opticalfilters 240. Optical fibers 210 transfer optical I/O to and from thearray of lasers 220 and photo detectors 230. Although described hereinusing optical fibers, in other embodiments optical fibers may bereplaced with plastic waveguides.

In one embodiment, the array of lasers 220 and photo detectors 230 forma single transceiver. In such an embodiment, the transceiver is ananti-symmetric transceiver used to perform bi-directional paralleloptic. A parallel optic transceiver is characterized as using one ormore fibers for transmission and one or more fibers for reception.Bi-directional refers to each waveguide/fiber transmitting light in bothdirections.

According to one embodiment, lasers 220 are vertical cavity surfaceemitting laser (VCSEL) lasers that perform optical to electricalconversions. Photo detectors 230 are PIN photodiodes that transformlight into a current.

In one embodiment, the transceiver includes the same number oftransmitters as receivers. The number of transmitters or receivers is amultiple of the number of fibers. Further, each fiber has the samenumber of transmitters and the same number of receivers. According toone embodiment, the minimum number of wavelengths for the transceiver isequal to the number of receivers plus the number of transmitters dividedby the number of fibers.

Additionally, on each fiber of the transceiver, the receivers andtransmitters are to operate at a different wavelength. The transmitternumbering (channel numbering) is arranged in the opposite way as thenumbering of a coupled receiver. Moreover, the path length and number offilters and connectors separating the transmitter from the receiver areidentical to provide an effective optical balance between all thechannels.

Referring to FIG. 2 as an example, the transceiver includes twelvelasers 220 and twelve photo detectors 230 that process two differentwavelengths to perform the bidirectional parallel optic functionality. Afirst set of six lasers drive optical I/O on to coupled fibers 210 a,while a second set of six lasers drive optical I/O on to coupled fibers210 b. Each set of fibers (210 a and 210 b) transfers two wavelengths(λ₁ and λ₂). For example, fibers 210 a transfers λ₁ upstream (e.g., fromlasers 220 towards photo detectors 230) and transfers λ₂ downstream(e.g., from photo detectors 230 towards lasers 220). Similarly, fibers210 b transfers λ₂ upstream and transfers λ₁ downstream.

In one embodiment, filters 240 are located near each laser 220 and photodetector 230. Filters 240 are chromatic filters reflect data transferredat one wavelength while allowing data transferred on the otherwavelengths to pass. For instance, downstream filters 240 (e.g., filtersnear photo detectors 230) reflect λ₂ signals carried on fibers 210 ainto photo detectors 230, while λ₂ signals are passed downstream.

FIG. 3 illustrates one embodiment of a bidirectional parallel opticallink coupling two anti-symmetrical bidirectional parallel optictransceivers. An anti-symmetrical transceiver is a first transceiver (A)that when connected back-to-back to an identical transceiver (B), eachindividual channel of transceiver A is connected to the correspondingchannel of transceiver B. For example, a transmitter#1 of transceiver Ais connected to receiver#1 of transceiver B, transmitter#1 oftransceiver B is connected to receiver#1 of transceiver A, transmitter#2of transceiver A is connected to receiver#2 of transceiver B,transmitter#2 of transceiver B is connected to receiver#2 of transceiverA and so forth. In one embodiment, each channel matches channel numbersand the specific wavelength.

As shown in FIG. 3, each transceiver (A or B) includes eighttransmitters (Tx1 to Tx8) and eight receivers (Rx1 to Rx8). Thetransceiver (A or B) also includes eight fibers. Each fiber is connectedto one transmitter and one receiver. On the transceiver (A or B), thetransmitters are ordered in the opposed way as the receivers.

Of the eight transmitters, four (Tx1 to Tx4) emit light at a wavelengthλ₁, while the other four (Tx5 to Tx8) emit at a wavelength λ₂. Of theeight receivers, four (Rx1 to Rx4) are sensitive to a wavelength λ₂ andfour (Rx5 to Rx8) are sensitive to a wavelength λ₁. Therefore on thetransceiver (A or B), Tx1 to Tx4 and Rxl to Rx4 operate at thewavelength λ₁ and Tx5 to Tx8 and Rx5 to Rx8 operate at the wavelengthλ_(2.)

By connecting transceiver A back-to-back to transceiver B, Tx1A isconnected to Rx1B at a wavelength λ₁; Tx8B is connected to Rx8A at awavelength λ₂; Tx2A is connected to Rx2B at a wavelength λ₁, . . . , . .. Tx8B is connected to Rx8A at a wavelength A₂. The transceiver (A or B)is perfectly anti-symmetric (transmitter/receiver pair and wavelength)and all optical path lengths are equal.

FIG. 4 illustrates another embodiment of a bi-directional paralleloptical link coupling two anti-symmetrical bi-directional parallel optictransceivers. In this embodiment, each transceiver (A or B) is builtwith sixteen transmitters (Tx1 to Tx16) and sixteen receivers (Rx1 toRx16). The transceiver (A or B) includes eight fibers. Each fiber isconnected to two transmitters and two receivers.

For this transceiver (A or B), the transmitters are ordered in theopposed way as the receivers. Of the sixteen transmitters, four (Tx1,Tx2, Tx11 and Tx12) emit light at a wavelength λ₁, four others (Tx3,Tx4, Tx9 and Tx10) emit at a wavelength λ₂, four others (Tx5, Tx6, Tx15and Tx16) emit at a wavelength λ₃, and the last four (Tx7, Tx8, Tx13 andTx4) emit at a wavelength λ4 _(.)

Of the sixteen receivers, four (Rx1, Rx2, Rx11 and Rx12) are sensitiveto a wavelength λ₁, four (Rx3, Rx4, Rx9 and Rx10) are sensitive to awavelength λ₂, four (Rx5, Rx6, Rx15 and Rx16) are sensitive to awavelength λ₃, and four others (Rx7, Rx8, Rx13 and Rx14) are sensitiveto a wavelength λ₄. Therefore on this transceiver (A or B), Tx1, Tx2,Tx11, Tx12, Rx1, Rx2, Rx11 and Rx12 work at the wavelength λ₁, Tx3, Tx4,Tx9, Tx10, Rx3, Rx4, Rx9 and Rx10 work at the wavelength λ₂, Tx5, Tx6,Tx15, Tx16, Rx5, Rx6, Rx15 and Rx16 work at the wavelength λ₃, and Tx7,Tx8, Tx13, Tx14, Rx7, Rx8, Rx13 and Rx14 work at the wavelength λ_(4.)

By connecting transceiver A back-to-back to transceiver B, Tx1A isconnected to Rx1B at a wavelength λ₁; Tx16B is connected to Rx16A at awavelength λ₃; Tx9A is connected to Rx9B at a wavelength λ₂, . . . , . .. Tx8A is connected to Rx8B at a wavelength λ₄. The transceiver (A or B)is perfectly anti-symmetric (transmitter/receiver pair and wavelength)and all optical path lengths are equal.

The above-described mechanism enables two transceivers to be opticallycoupled via a single set of waveguides. As a result, the number ofwaveguides or fibers in an optical communication link is reduced.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asthe invention.

1. a system comprising: a first optical transceiver having a first setof transmitters and a first set of receivers; and a second opticaltransceiver having a second set of transmitters coupledanti-symmetrically to the first set of receivers of the first opticaltransceiver and a second set of receivers coupled anti-symmetrically tothe first set of transmitters of the first optical transceiver.
 2. Thesystem of claim 1 wherein the first set of transmitters and second setof receivers operate at a first wavelength and the second set oftransmitters and first set of receivers operate at a second wavelength.3. The system of claim 2 wherein a first transmitter of the firstoptical transceiver is coupled to a first receiver of the second opticaltransceiver and a second transmitter of the first optical transceiver iscoupled to a second receiver of the second optical transceiver.
 4. Thesystem of claim 3 wherein a first transmitter of the second opticaltransceiver is coupled to a first receiver of the first opticaltransceiver and a second transmitter of the first optical transceiver iscoupled to a second receiver of the first optical transceiver.
 5. Thesystem of claim 4 wherein the first transmitter of the second opticaltransceiver is coupled to a first receiver of the first opticaltransceiver and a second transmitter of the first optical transceiver iscoupled to a second receiver of the first optical transceiver.
 6. Thesystem of claim 4 further comprising a set of optical waveguides coupledbetween the first optical transceiver and the second opticaltransceiver, each optical waveguide in the set of optical waveguides totransfer optical data of the first wavelength and optical data of thesecond wavelength between the first optical transceiver and the secondoptical transceiver.
 7. The system of claim 6 further wherein the set ofoptical waveguides comprises: a first optical waveguide coupled betweenthe first transmitter of the first optical transceiver and the firstreceiver of the second optical transceiver; and a second opticalwaveguide coupled between first transmitter of the second opticaltransceiver is coupled to a first receiver of the first opticaltransceiver.
 8. The system of claim 6 further comprising: a first filterto extract optical data having the first wavelength from the firsttransmitter of the first set of transmitters on to the first opticalwaveguide; and a second filter to extract optical data having the secondwavelength from the first optical waveguide into the first receiver ofthe first set of receivers.
 9. The system of claim 3 wherein the firsttransmitter and the second transmitter are vertical cavity surfaceemitting laser (VCSEL) lasers.
 10. A method comprising: transmittingoptical data having a first wavelength from a first transmitter at afirst transceiver to a first receiver at a second transceiver via afirst optical waveguide; and transmitting optical data having a secondwavelength from a second transmitter at the second transceiver to asecond receiver at the first transceiver via the first opticalwaveguide.
 11. The method of claim 10 further comprising: extracting theoptical data having the first wavelength from the first transmitter onto the first optical waveguide; and extracting the optical data havingthe second wavelength from the first optical waveguide in to the secondreceiver.
 12. The method of claim 10 further comprising: transmittingoptical data having the first wavelength from a third transmitter at thefirst transceiver to a third receiver at the second transceiver via asecond optical waveguide; and transmitting optical data having thesecond wavelength from a fourth transmitter at the second transceiver toa fourth receiver at the first transceiver via the second opticalwaveguide.
 13. An optical transceiver comprising: a first transmitter totransmit optical data having a first wavelength; and a first receiver toreceive optical data having a second wavelength.
 14. The transceiver ofclaim 13 further comprising: a second transmitter to transmit opticaldata having the first wavelength; and a second receiver to receiveoptical having the second wavelength.
 15. The transceiver of claim 14wherein the first transmitter and the first receiver are coupled via afirst optical waveguide and the second transmitter and the secondreceiver are coupled via a second optical waveguide.
 16. The transceiverof claim 15 further comprising: a first filter to extract optical datahaving the first wavelength from the first transmitter on to the firstoptical waveguide; and a second filter to extract optical data havingthe second wavelength from the first optical waveguide into the firstreceiver.
 17. The transceiver of claim 13 wherein the first transmitterand the second transmitter are vertical cavity surface emitting laser(VCSEL) lasers.
 18. The transceiver of claim 13 wherein the firstreceiver and the second receiver are PIN photodiodes.
 19. Thetransceiver of claim 16 wherein the first filter and the second filterare chromatic filters.
 20. The transceiver of claim 14 furthercomprising: a third transmitter to transmit optical data having thefirst wavelength; and a third receiver to receive optical having thesecond wavelength.